1. Field of the Invention
The invention relates to a bolometric detector with an antenna as well as to a method for manufacturing such a detector.
The invention is more specifically applied to the passive detection of electromagnetic waves with millimetric wavelengths.
The detection is said to be passive when the observed scene emits the signal to be detected, on its own, either directly by its own emission of a grey body which it forms, or indirectly, by reflection on another grey body.
2. Discussion of the Background
Passive detection of millimetric waves is presently based on two different principles.
According to a first principle, the electromagnetic wave is detected by an antenna so as to generate an electric signal, the processing of which is carried out by an electronic circuit operating at the wave's frequency. According to a second principle, the electromagnetic wave is detected by an antenna so as to generate a heat flux which is measured.
A disadvantage of the detectors operating according to the first principle is that they are limited in frequency.
Indeed, the technologies used for producing such circuits, such as technologies based on gallium arsenide (AsGa) or indium phosphide (InP), are presently inaccessible at frequencies higher than 100 GHz, for example.
Moreover, in the case when the detectors have to be brought together as a matrix of n×m detectors, such circuits have high power dissipation, of the order of 1 Watt for a 32×32 matrix, for example. This is also a disadvantage.
Detectors operating according to the second principle form the class of bolometric detectors.
Bolometric detection is such that the power of the electromagnetic wave which is collected by the antenna is converted in a resistive load into heating power which is measured. Measurement of heating power is performed by means of a thermal conductance which converts the heat flux into a rise in temperature relatively to a reference temperature. The thus determined rise in temperature is converted into an electric signal by a component, a so-called “thermometric component”.
A bolometric detector according to the known art is described in the article entitled “Antenna-coupled bolometer with a micromachined—beam thermal link” and published in the journal “Appl. Phys. Lett. 71 (16)” as of Oct. 20th 1997.
Such a bolometric detector comprises:                a receiving antenna for collecting electromagnetic waves,        a resistive load for converting the collected electromagnetic power into heating power,        a transmission line or guide for transmitting the electromagnetic waves received by the antenna to the resistive load,        means for measuring the heating power.        
The presence of the transmission line or guide between the receiving antenna and the resistive load has several disadvantages. A first disadvantage is that it participates not insignificantly to the bulkiness of the bolometric detector. Another disadvantage is the difficulty in producing such a line or guide for high frequency circuits, such as for frequencies beyond 50 GHz.